An adhesive in a form of paste and a product wherein an adhesive is applied to a heat-resistant material have been known as adhesives for fixing treatment of electric and electronic parts such as semiconductor chips, base plates and lead frames. Thermosetting resins such as epoxy resin, acrylic resin and rubber-phenol resin have been used as such adhesives, but they require high temperature and long time for setting by heating and workability for adhesion is poor. In addition, there are various problems such that, upon heat setting, large amount of volatile components are produced whereby lead is stained, and cracks generate upon a reflow soldering due to their high hygroscopicity. Thus, the conventional adhesives cannot be said to have a high reliability necessary for the fixing treatment of electric and electronic parts, and up to now, no satisfactory adhesives have been available.
Incidentally, a film adhesive of a hot melt type using a thermoplastic polyimide resin is able to adhere by heating with short time and an additional setting after adhesion is not necessary. However, its glass transition temperature is high and very high temperature is required for processing, so that there is a large possibility of thermal damage to an adherend.
On the other hand, when an adhesive having a low glass transition temperature is used to impart a processability at low temperature, there is a problem that heat resistance is low and reliability is significantly low. For example, polycarbodiimide has a low glass transition temperature and exhibits excellent adhesion and processability at low temperature, but its reliability is poor and, when exposed to an atmosphere at high temperature and high pressure for dozens of hours, the adhesive strength is lost. In order to solve such a disadvantage in polycarbodiimide, a siloxane skeleton may be introduced into its molecule to improve the relaibility. However, most of the commercially available siloxane-modified diisocyanate used as a monomer raw material is aliphatic, and therefore, there is a problem on reactivity when producing the polycarbodiimide. Moreover, synthesis of the siloxane-modified arylic diisocyanates is usually difficult and the products are unstable and are unable to be practically used. Accordingly, there has been a demand to improve the moisture resistance by blending polycarbodiimide with other polymers rather than by using polycarbodiimide alone.
An example of the substances that physical properties may be improved by blending the same with polycarbodiimide is bisaryl-substituted nadiimide. JP-A-7-286140 (the term "JP-A" used herein means an "unexamined Japanese patent application") proposes thermosetting coating materials having excellent heat resistance comprising the above-described nadiimide, JP-A-7-258353 proposes resin compositions comprising a blend of the above-described nadiimide and bismaleimide, and JP-A-7-330872 proposes resin compositions comprising a blend of the above described nadiimide and epoxy resin. However, no satisfactory result has been achieved in adhesive strength and flexibility when used as an adhesive.
Further, JP-A-62-1714, 5-239427 and 5-320611 propose adhesive resin compositions obtained by blending epoxy resin with polycarbodiimide resin. However, there is a problem in storage stability and hygroscopicity of epoxy resin, and no satisfactory result is achieved.
On the other hand, although polyimides usually have excellent heat resistance, in many cases they are insoluble in organic solvents and are not miscible with polycarbodiimide. Usually they are often used in the form of a solution of polyamide acids which are precursors thereof in order to improve the miscibility of polyimide with other polymers. However, when the polymer to be mixed therewith is polycarbodiimide, there is a problem that it reacts with the carboxyl groups in the polyamide acid whereupon the stability of the solution becomes significantly poor.